Transition and Inner Transition Elements
Transition and Inner Transition Elements tests electronic configuration, variable oxidation states, magnetic moments, colour, catalysis and the lanthanoid contraction. Numerical questions on spin-only magnetic moments are common.
d-block rules
- General configuration is (n-1)d1-10 ns1-2; Cr is [Ar]3d5 4s1 and Cu is [Ar]3d10 4s1 because half-filled and fully filled d subshells are more stable.
- Transition metals show variable oxidation states because 4s and 3d electrons have similar energies.
- Colour arises from d-d transitions; Sc3+ and Zn2+ are colourless because their d subshells are empty or full.
- Paramagnetism depends on unpaired electrons: mu = sqrt[n(n+2)] BM.
Lanthanoids and actinoids
- Lanthanoids fill 4f; the common state is +3, with Ce4+ and Eu2+ important exceptions.
- Lanthanoid contraction is the steady decrease in size due to poor shielding by 4f electrons.
- Actinoids fill 5f, are radioactive, and show a wider range of oxidation states (+3 to +7).
Worked example
Calculate the spin-only magnetic moment of Fe3+. Reasoning: Fe is [Ar]3d6 4s2; Fe3+ loses three electrons, giving [Ar]3d5. There are five unpaired electrons, n = 5. mu = sqrt(5 x 7) = sqrt(35) = 5.92 BM. The ion is paramagnetic.
Traps
- Zn is in the d-block but Zn2+ is d10 and not a typical transition-metal ion.
- Use unpaired electrons, not total d electrons, in the magnetic moment formula.
- Ce4+ is stable because it has a noble-gas configuration; do not call all lanthanoids only +3.
- Lanthanoid contraction is not caused by increasing nuclear charge alone; shielding by 4f electrons is poor.